Cameras with higher resolution above 1.3 megapixels (MP) generally have increased thickness due to the optical characteristics of the lens mechanisms, particular camera lenses with auto focus and zoom capabilities. With the size pressures on new products like Motorola, Inc.'s Motorize V3® phone, the flip thickness has been reduced from around 9 to 10 mm three years ago to about 5 to 6 mm today. The thicker higher resolution cameras (that can be 10 to 13 mm thick) no longer fit in the flip housing portions of the phones which was the typical location for the cameras. There are many examples of such camera having the camera in the flip portion such as Motorola's A840 that includes a 1.2 MP camera.
Some phones have avoided this issue by placing the camera in a hinge mechanism of a clam style phone so that they can hide the camera in the base of the phone while making it look like it is on the flip. Since there is more room in the typical base housing of a phone, a phone can utilize this extra volume for the camera so that the size of the flip is not impacted. However, a camera in the base housing portion of the phone would have to be angled in such a way that it is perpendicular to the phone's display to operate effectively. With a display on the (internal) flip housing portion and a camera on a (external) base portion, there would generally be a misalignment problem between the viewing angles of the camera and the corresponding display.
There are several flip phones with pivoting cameras on the hinge of a phone and there are numerous monolith, sliders and rotating display phones with the camera on the base housing portion. However, these phones have the camera perpendicular to the display by the basis of the form factor. There are no known flip phone products with the camera in the base.